This invention relates generally to micro-electromechanical devices. More particularly, this invention relates to a micro-electromechanical cantilever whose motion is controlled by torsional beams and a counterweight.
Micromachines (also called micromechanical devices or micro-electromechanical devices) are small (micron scale) machines that promise to miniaturize instrumentation in the same way microelectronics have miniaturized electronic circuits. As used herein, the term micromachine refers to any three-dimensional object having one or more sub-millimeter dimensions formed using semiconductor processing techniques.
One form of micromachine is a cantilever. Cantilevers are widely used in scanning electronic microscopes. Recently, cantilevers have been incorporated into vertical cavity optical structures. Vertical cavity optical structures offer the advantages of single longitudinal mode operation, batch processing, two-dimensional array formation and cylindrical symmetry. The cavity length of such devices is small enough to allow for continuous tuning, rather than discrete mode hoping.
One type of vertical cavity optical structure is the vertical-cavity surface-emitting laser (VCSEL). VCSELs are used as light sources in a variety of electronic applications including fiber optic communications, laser printing, and optical data storage.
A VCSEL is an injection diode laser where the laser oscillation and output occur normal to a semiconductor pn junction plane. In edge-emitting laser diodes, the laser oscillation and output occur along the semiconductor pn junction. VCSELs have many advantages compared to edge-emitting laser diodes. These advantages include a low divergence circular output, single longitudinal mode operation, and high two-dimensional packing density.
In view of these advantages, there are ongoing efforts to utilize vertical cavity optical structures to replace bulk optical components. In comparison to bulk optical components, vertical cavity optical structures offer the advantages of lower cost, power and size.
One problem with current vertical cavity optical structures is tuning range. The tuning range of existing tunable vertical cavity structures is limited by the range of movement available in electrostatically actuated cantilevers. It would be highly desirable to extend the tunable range of the cantilever structure. Another problem with prior art vertical cavity optical structures utilizing cantilevers or multiply supported structures is that they collide with the device substrate upon reaching a bias point instability.
Overcoming these prior art problems associated with vertical cavity optical structures would facilitate their use in evolving commercial applications. For example, the growing demand for telecommunications bandwidth requires improved fiber optic communication links. Improved fiber optic communication links will enable technologies such as Dense Wavelength Division Multiplexing.
In view of the foregoing, it would be highly desirable to provide an improved vertical cavity optical structure with increased cantilever actuation range. Ideally, such a device would mitigate the problem of a cantilever colliding with its underlying substrate.
The invention includes an optical micro-electromechanical device. The optical micro-electromechanical device includes a substrate and a mirror assembly suspended above the substrate. The mirror assembly includes a torsional beam and a cantilever. The cantilever includes a cantilever first end and a cantilever second end. The cantilever first end is attached to the torsional beam. The cantilever second end supports a mirror head. A connector is attached to the torsional beam. A counterweight is attached to the connector.
The invention also includes a method of operating an optical micro-electromechanical device. The method includes the step of positioning a mirror assembly over a substrate, where the mirror assembly includes a torsional beam attached to the substrate, a cantilever with a cantilever first end and a cantilever second end, the cantilever first end being attached to the torsional beam, and the cantilever second end supporting a mirror head. A connector is attached to the torsional beam and a counterweight is attached to the connector. An electrical bias is applied to the substrate to create an electrostatic attraction between the counterweight and the substrate, which causes the torsional beam to rotate and thereby re-reposition the mirror head.
The invention provides an improved vertical cavity optical structure with increased cantilever actuation range. The vertical cavity optical structure can be operated as a laser, a detector, or a filter. The structure allows one to create a red-shift of filter wavelength and a blue-shift of filter wavelength. The device mitigates the problem of a cantilever colliding with its underlying substrate through the use of an isolation region, which may be implemented as an electrical isolation region through doping, through a passivation surface, or through spatial isolation. A counterweight configured with apertures facilitates fabrication.